prevent duplicate services from being created

app/models/service.rb

@@ -6,6 +6,7 @@ class Service < ActiveRecord::Base
   include ActionView::Helpers::TextHelper
 
   belongs_to :user
+  validates_uniqueness_of :uid, :scope => :type
   has_many :service_users, :dependent => :destroy
 
   def public_message(post, length, url = "")

spec/models/service_spec.rb

@@ -9,6 +9,13 @@ describe Service do
     @user.services << @service
   end
 
+  it 'is unique to a user by service type and uid' do
+    @service.save
+    @user.services << Services::Facebook.new(:access_token => "yeah")
+    @user.services[1].valid?.should be_false
+
+  end
+
   it 'destroys the associated service_user' do
     @service.service_users = [ServiceUser.create(:service_id => @service.id,
                                                  :uid => "abc123",